Microwave electron beam tubes



March 1970 c. N. OLOUGHLIN ETAL 3,500,111

I MICROWAVE ELECTRON BEAM TUBES Filed May 1, 196'! I F/GJ.

lg/FNTOR? MW .5) 5m My; flaw/ATTORNEYS United States Patent 3,500,111 MICROWAVE ELECTRON BEAM TUBES Cian Noel OLoughlin, Chelmsford, and Geoifrey Thomas 'Clayworth, Great Baddow, England, assignors t0 English Electric Valve Company Limited, London, England, a British company Filed May 1, 1967, Ser. No. 635,070 'Claims priority, application Great Britain, Mar. 31, 1967, 20,403/ 66 Int. Cl. H01j 23/20, 23/02 US. Cl. 315-552 6 Claims ABSTRACT OF THE DISCLOSURE A microwave electron beam tube of the kind in which the high frequency inter-action section is insulated from the collector section by a gap, between the sections, in a tubular member through which the electric beam passes is provided with a metallic member which tncircles the tube in neighbourhood of the gap. This metallic member is electrically connected to the tubular member on one side of the gap and a second metallic member is provided similarly encircling the tube, but connected to the tubular member on the other side of the gap. The metallic members sandwich between them a member of dielectric material so as to constitute a condenser which is outside the evacuated envelope of the tube and is in shunt with the gap.

This invention relates to microwave electron beam tubes such as klystrons and travelling wave tubes. More particularly the invention relates to microwave electron beam tubes of the kind in which the so-called body of the tube, i.e. high frequency inter-action section thereof, is insulated from the collector section thereof by a gap across which the electron beam passes on its way to the collector.

The invention is illustrated in and explained in connection with the accompanying drawings. In the figures FIGURE 1 is a schematic and highly simplified representation of a typical known klystron and is provided for purposes of explanation only; FIGURE 2 is a view of an embodiment of the present invention showing a klystron only to the extent necessary to an understanding of the present invention; and FIGURE 3 shows a modification of the klystron of FIGURE 2.

In the usual present day construction adopted for a klystron the tube consists of three main sections as represented in FIGURE 1. Section 1 contains the electron gun from which an electron beam is projected through section 2 to the collector electrode section 3. Section 2-usually called the body of the tubecontains a high frequency interaction structure of any of a variety of known forms, and section 3 contains the collector electrode by which the electrons of the beam are ultimately collected. In passing through the interaction structure the electrons of the beam interact with a high frequency input signal to produce amplification in the well known manner. Section 2 is normally at earth potential whereas section 3 is at a higher potential and good insulation between these sections is necessary. This is normally achieved by interrupt ing, between the sections 2 and 3, the copper tube 4 through which the electron beam passes, so as to leave a gap '5 which ensures the necessary insulation. The con tinuity of the vacuum-retaining envelope of the tube is ensured by some such means as a ceramic cylinder 6 fixed in a vacuum tight manner to and between the two metal annular members 7, 8, secured vacuum tight on the copper tube 4 on either side of the gap therein.

If no steps were taken to prevent it, the passage of the beam emerging from the interaction section 2 across the gap 5 would cause the radiation of substantial amounts of high frequency energy sufficient to cause troublesome interference with nearby electronic or other high frequency apparatus. In order to prevent this it is customary practice to shunt the gap 5 by a capacitance provided by a vacuum-dielectric condenser constituted by a pair of closely spaced electrodes (not shown) situated inside the evacuated envelope of the tube. The amount of space available inside the evacuated envelope is, however, limited and this correspondingly limits the permissible areas of and therefore the capacitance of the electrodes of the condenser. These electrodes have therefore to be closely spaced in order to provide a sufficiently large capacitance to shunt the gap adequately. However, because they are near the gap they are subjected to electron bombardment and become heated. This heat is ditficult to remove so that distortion of the electrodes with consequent serious risk of arcing-over or short-circuiting during operation. If a short circuit occurs between the body 2 and the collector 3 the tube may be seriously damaged and rendered useless. The present invention seeks to overcome the foregoing defects and difficulties in a tube which is constructionally robust, reliable and comparatively cheap and easy to manufacture by factory methods.

According to this invention in its broadest aspect a microwave electron beam tube of the kind referred to has the gap thereof shunted by a condenser with a dielectric of solid material the electrodes of said condenser being outside the evacuated envelope of the tube and encircling the tube in the neighbourhood of said gap.

According to a feature of this invention a microwave electron beam tube of the kind in Which the high frequency interaction section thereof is insulated from the collector section thereof by a gap, situated between said sections, in a metallic tubular member through which the electron beam passes includes a metallic member encircling the tube in the neighbourhood of said gap and electrically connected to said tubular member on one side of said gap, and a second metallic member also encircling the tube in the neighbourhood of said gap but electrically connected to the tubular member on the other side of said gap, said metallic members being spaced apart by and sandwiching between them a member of solid dielectric material, the three members constituting a condenser which has a dielectric of solid material and which is outside the evacuated envelope of the tube and is in shunt with said gap.

The three members constituting the condensertwo of them metallic and the third of solid dielectric-may take any of a variety of forms. In one type of construction the members are of plate-like form. In another construction they are of tubular or cylindrical form.

In one embodiment of the invention the metal members are plate members of L section each consisting of an annular portion with a short cylindrical portion extending from the inner edge of the annular portion, and the cylindrical portion of one metallic member is electrically and mechanically united with a metallic annular member in electrical connection with the tubular member on one side of the gap, the cylindrical portion of the other metallic member being electrically connected by a spring contact with a second metallic annular member in electrical connection with the tubular member on the other side of the gap.

In the embodiment of the invention shown in FIG- URE 2 the collector section, the metallic (normally copper) tube through which the beam passes, the gap, the ceramic cylinder, and the two metallic annular members are referenced 3, 4, 5, 6, 7 and 8 respectively and correspond to the similarly referenced parts of FIGURE 1. The gun section (1 in FIGURE 1) of the tube is not shown and only the end of the collector section 2 of the tube is shown. Fixed on the tubular member 4 at a position between the annular member 8 and the adjacent end of the intersection section 2 is a metal annular member 9. Fixed to the tubular member 4 on the other side of the gap 5 and at a position between the annular member 7 and the collector section 3 is another metal annular member 10 of somewhat smaller diameter than that of the member 9. The outer edge of member 10 is peripherically grooved and a coiled metal spring 11 is seated in the groove.

A metal plate member 12 of L section and consisting of an annular portion 12A and a cylindrical portion 123 is fixed, at the outer end of its cylindrical portion to the outer portion of the member 9. A second metal plate member 13 of similar shape to that of the member 12 is spaced from said member 12 by a solid dielectric plate member 14 again of similar shape and which is sandwiched between the members 12 and 13. The inner face of the cylindrical portion of the member 13 is in contact with the spring 11 as shown and thus is in electrical connection with the member 10. The parts 12-14-13 thus constitute a solid dielectric condenser which is outside the evacuated envelope of the tube and can readily be made of adequate capacitance to prevent undesired radiation of high frequency energy from the gap 5 across which it is shunted while the danger of arc-over or short circuiting which exists with the known arrangements hereinbefore described is avoided. In order to facilitate inderstanding of FIGURE 2 the members 13 and 14 are shown cross-hatched.

In the embodiment of FIGURE 2 the condenser constituted by the parts 12-14-13 is of plate like form i.e. :he electrodes are, in the main, plates of disc form. The nodification shown in FIGURE 3 will, it is thought, he Largely self-explanatory from the said figure. As will be ipparent it differs from the embodiment of FIGURE 2 n that the condenser, constituted by the parts referenced [2, 14' and 13', is of tubular or cylindrical form, the :lectrodes 12, 13 being cylindrical.

We claim:

1. An improved electron beam tube having an evacuated envelope, a high frequency section, a collector sec- .ion, and a gap situated between said sections in a tubular nember through which an electron beam passes, the im- Jrovement comprising a first metallic member at least )artially encircling the tube and positioned outside said :vacuated envelope in the neighborhood of said gap and :lectrically connected to said tubular member on one side )f said gap, and a second metallic member atleast parially encircling the tube and positioned outside said :vacuated envelope in the neighborhood of said gap and :lectrically connected to the tubular member on the other side of said gap, said members being spaced apart by and sandwiching between them a member of solid dielectric material, the three members constituting a condenser.

2. A microwave electron beam tube of the kind in which the high frequency interaction section thereof is insulated from the collector section thereof by a gap situated between said sections, in a metallic tubular member through which the electron beam passes said tube including a metallic member encircling the tube in the neighbourhood of said gap and electrically connected to said tubular member on one side of said gap, and a second metallic member also encircling the tube in the neighbourhood of said gap but electrically connected to the tubular member on the other side of said gap, said metallic members being spaced apart by and sandwiching between them a member of solid dielectric material, the three members constituting a condenser which has a dielectric of solid material and which is outside the evacuated envelope of the tube and is in shunt with said gap.

3. A tube as claimed in claim 2 wherein the condenser is of plate form.

4. A tube as claimed in claim 2 wherein the condenser is of tubular form.

5. A tube as claimed in claim 3 wherein the metal members are plate members of L section each consisting of an annular portion with a short cylindrical portion extending from the inner edge of the annular portion, and the cylindrical portion of one metallic member is electrically and mechanically united with a metallic annular member in electrical connection with the tubular member on one side of the gap, the cylindrical portion of the other metallic member being electrically connected by a spring contact with a second metallic annular member in electrical connection with the tubular member on the other side side of the gap.

6. A tube as claimed in claim 4 wherein the metal members and the member of solid dielectric are co-axial cylinders extending parallel to the tube axis round the collector section of the tube.

References Cited UNITED STATES PATENTS 3,274,430 9/1966 El-Hefni 315-5.52 X

JAMES W. LAWRENCE, Primary Examiner C. R. CAMPBELL, Assistant Examiner US. Cl. X.R. 3155.38 

